Destructive operations

["Scott E. Fahlman" <Fahlman@C.CS.CMU.EDU>]

In my view, when a constant appears in code, the compiler is free to
store this in read-only space or do other strange things that depend on
the constantness of the constant.  Many useful optimizaitons depend on
this.  I thought that I could find something in the manual that implied
this clearly, but a cursory search failed.  The description of
DEFCONSTANT says that the compiler assume that such constants will stay
put, but I found nothing about other constants, such as '(a b c), that
might appear in the body of the code.  Still, I think that we must allow
the compiler to assume that these things will not be altered
destructively.  You can always store the list in a variable if you want
it to be malleable.

CLtL doesn't say much about what the compiler is required to do or not
do.  A subcommittee of X3J13 has been set up to formulate
recommendations on how to fix this.  This is one of the issues that they
should address.

-- Scott